The Demiplane of Nightmares is a demiplane coterminous with both the Ethereal Plane and the Region of Dreams.
The boundary between the Demiplane of Nightmares and the Far Realm is very thin, and Far Realm taint continually leaks into the demiplane, corrupting all it touches
Description
The Demiplane of Nightmares is described as a place whose angles, geometry, and inhabitants seem disturbing and repelling by human standards. On this plane, a traveler's darkest thoughts and fears become reality.
Inhabitants
Inhabitants of the Demiplane of Nightmares include neh-thalggu, diaboli, feyrs, nagpas, maelephants, and others.
The diaboli (singular: diabolus) live out their lives on the demiplane much like humans do in the Realms, farming and hunting, building villages and towns, and interacting with their neighbors in ways that can be either peaceful or violent, depending on the situation. Their settlements are ramshackle and random, resembling ruins to human eyes. Diabolus buildings tilt at precarious angles and are arranged with seemingly no regard to defensibility, practicality, or convenience. Diaboli devote most of their resources to philosophy, art, and fighting against the taint of the Far Realm. They hate and fear humans, viewing them as hideous demons or devils. They have proven shy about emigrating to Toril.
While neh-thalggu are not native to the Demiplane of Nightmares, they occupy a place in diabolus myth and legend roughly equivalent to the place dragons hold in human stories.
History
In -681 DR, Netherese arcanists emigrated to the Demiplane of Nightmares, where the energies infusing the plane twisted their descendants until they evolved into the Night Parade.
Much more recently (exactly when is unclear), members of the Night Parade opened portals back to the Realms, where they began infiltrating cities such as Calimport.